358  PRE-OAMBRTAN    GEOLOGY    OF    NORTH    AMERICA. 
Westward  from  Port  Arthur,  along  the  international  boundary  to 
Gunflint  Lake,  the  Animikie  rocks  are  found  to  rest  un^onformably 
upon  the  principal  sedimentary  rocks  of  the  Vermilion  district,  the 
Knife  Lake  slate,  Ogishke  conglomerate,  and  Stuntz  conglomerate, 
similar  to  the  Dore  conglomerate  of  the  Michipicoten  district. 
Beneath  them  is  a  complex  of  greenstones,  green  schists,  and  iron 
formation,  similar  in  all  respects  to  that  beneath  the  Dore  conglom- 
erate of  the  Michipicoten  district.  These  are  typical  Keewatin.  The 
conglomerate  and  slate  series  above  is  accordingly  placed  in  the  lower- 
middle  Huronian.  Granites  intrusive  into  the  Keewatin  are  classed 
as  Laurentian. 
West-southwest  from  Gunflint  Lake,  in  the  Mesabi  district,  the 
Animikie  group  is  found  to  contain  the  great  iron-bearing  member  of 
the  Mesabi  iron  range.  Here  also  the  Animikie  overlies  a  graywacke 
and  slate  group  intruded  by  granite,  similar  in  all  respects  to  the  group 
underlying  the  Animikie  in  the  Vermilion  district.  It  is  accordingly 
assigned  to  the  lower-middle  Huronian.  Beneath  this  lower-middle 
Huronian  there  is  a  complex  of  greenstones  and  green  schists  showing 
characters  identical  with  those  exhibited  in  the  Keewatin  of  the  Ver- 
milion district,  and  hence  it  is  so  classed. 
In  central  Minnesota  a  considerable  body  of  sediments,  typically 
exposed  at  Carlton  and  Cloquet,  has  been  referred  to  the  upper  Hu- 
ronian because  of  their  lithological  and  structural  similarity  to  the 
upper  Huronian  of  the  Mesabi  district,  and  because  they  have  a  posi- 
tion which  would  indicate  them  to  be  part  of  the  southern  margin  of 
the  syncline  of  Animikie  rocks  supposed  to  extend  south  from  the 
Mesabi  district. 
The  similarity  in  lithology,  succession,  and  structure  of  the  Mesabi 
iron-bearing  strata  with  those  of  the  Gogebic  district,  and  the  fact 
that  the  Mesabi  strata  dip  gently  to  the  south  and  the  Gogebic  rather 
steeply  to  the  north,  conforming  to  the  general  synclinal  structure  of 
the  Lake  Superior  basin,  leave  little  doubt  that  the  Animikie  or 
upper  Huronian  extends  to  the  south  shore.  A  sketch  map  showing 
a  supposed  connection  of  the  Mesabi  and  Gogebic  districts  on  the 
hypothesis  of  synclinal  structure  was  given  in  Monograph  XLIII, 
published  in  1903.  Since  that  time  exploration  and  development 
have  shown  the  existence  of  an  iron  formation,  probably  of  upper 
Huronian  age,  in  the  Cuyuna  range  on  the  south  side  of  this  hypo- 
thetical syncline. 
Beneath  the  upper  Huronian  of  the  Gogebic  district,  with  pro- 
found unconformity,  is  a  limestone  and  a  quartzite  formation  repre- 
senting the  remnant  of  a  lower  group.  Unconformably  beneath  this 
in  turn  is  a  complex  of  greenstones  and  green  schists,  undoubtedly 
Keewatin,  and  granites  of  Laurentian  age.  The  limestone  and 
quartzite  are  correlated  with  the  lower  Huronian  of  the  Marquette 
district  on  the  basis  of  lithology,  succession,  and  relations. 
